1. Field of the Invention
The present invention relates to a through electrode and a method for forming the same, and particularly relates to a through electrode adapted to fill a small hole with a conductive material and a method for forming the same.
2. Description of the Related Art
Electronic devices having three-dimensional structures, such as micromachine packages and interposers, called as MEMS (Micro Electro Mechanical Systems), and utilizing semiconductor microprocessing technologies are known. In recent years, techniques for forming through electrodes that connect an upper wiring pattern to a lower wiring pattern in such an electronic device have been developed. For example, in some interposers, through electrodes are formed in through holes extending between an upper face and a lower face of a substrate so as to provide electrical connection between wiring patterns (see, for example, Japanese Patent Laid-Open Publication No. 1-258457).
This publication discloses a method for filling through holes, which are formed in a substrate covered with insulating film, with metal by plating. According to this method, a seed layer is formed on an upper face of a substrate by a sputtering method. Then, an electrode for plating is brought into contact with an upper face of the seed layer to deposit conductive metal, such as Cu, onto the surface of the seed layer using an electrolytic plating method. A conductor layer formed of the conductive metal is then grown, so that the through holes are filled with metal.
However, the method described above has a problem that, because the conductor layer formed on the surface of the seed layer is formed on the inner surfaces of the through holes and grows on the inner surfaces of the through holes, voids are formed near the center of the individual through holes along with the growth of the conductor layer.
Especially, in the case of micromachine packages, when the diameter of a through hole relative to the thickness of a substrate is small and accordingly the aspect ratio (thickness/hole diameter) is high, it is difficult to form a through electrode in such a small through hole.